Hydraulic devices for removing tubes drawn on a long mandrel



June 16, 1964 M. FERRET 3,137,384

HYDRAULIC DEVICES FOR REMOVING TUBES DRAWN ON A LONG MANDREL OriginalFiled April 23, 1957 s Sheets-Sheet 1 mvm June 16, 1964 FERRET 3,137,384

HYDRAULIC DEVICES FOR REMOVINQ TUBES DRAWN ON A LONG MANDREL OriginalFiled April 23, 1957 3 Sheets-Sheet 2 4 12 ,za- V! 278 In uen+ov June16, 1964 M. PERRET 3,137,384

HYDRAULIC DEVICES FOR REMOVING TUBES DRAWN ON A LONG MANDREL. OriginalFiled April 23, 1957 3 Sheets-Sheet 3 1x 1 /918 F 20 55 62 .5/ 49 54 6542 1 36 47 50 I l (a J M United States Patent 3,137,384 HYDRAULICDEVICES FOR REMOVING TUBES DRAWN ON A LONG MANDREL Marcel Perret,Saint-Maude, Seine, Fi'ance, assignor to Trefileries et Laminoirs dePrecision Gilby-Fodor (Societe Anonyme), Rueil-Malmaison, Seine, France,a company of France Original application Apr. 23, 1957, Ser. No.654,594, now Patent No. 2,983,366, dated May 9, 1961. Divided and thisapplication Apr. 10, 1961, Ser. No. 101,834

Claims priority, application France Apr. 25, 1956 2 Claims. (Cl. 205-7)This application is a division of Serial No. 654,594, filed April 23,1957, now Patent No. 2,983,366.

It is well known that the drawing of metal tubes with the object ofreducing their diameter and Wall thickness, or with a view to givingthem a section of pre-determined form, is effected by passage through adie, using an internal indeformable mandrel.

Depending on whether this mandrel is fixed or moves with the tube, thedrawing processes are respectively termed in the industry drawing on anoval mandrel or drawing on a long mandrel."

The manner of plastic deformation of the metal is different in the twoprocesses, since when drawing over an oval mandrel, internal friction isproduced, this being avoided in drawing over a long mandrel by reason ofthe movement of the mandrel. The result is that, for the same reductionin section, and all other conditions remaining the same, the portion ofthe tube on the delivery side of the die is subjected during drawingover an oval mandrel to a stress which is substantially greater thanthat which is encountered in drawing over a long mandrel.

This state of alfairs results in limitations in the process of drawingover oval mandrels, amongst others, in the reduction of section perpass, which is smaller than for drawing over long mandrels, and in thecase of tubes with thin walls defined by a ratio:

external diameter internal diameter less than or equal to 1.02, inwhichtubes the low mechanical strength does not enable them to withstand thehigher drawing stresses necessary for drawing over an oval mandrel.

In spite of all this, drawing over oval mandrels is the method mostgenerally adopted for the manufacture of tubes with normal wallthickness, since it gives a high production output, due to the fact thatthe oval mandrel is automatically disengaged from the interior of thetube at the end of the operation.

The rates of production output are in fact very much lower in the caseof drawing over long mandrels, since this process is slowed down by thesubsequent operation of removal of the mandrel, which, under the bestconditions, requires twice the time needed for the drawing operationproper.

It will be recalled that the operation of removal of the mandrelconsists actually in slightly expanding the diameter of the tube by apermanent deformation, (the tube having been strongly compressed andremaining closely applied against the mandrel during the previousdrawing operation), in order to enable the said mandrel to be extractedlater. This operation is usually carried out on machines with rollers ofsuitable shape which apply to the tube a pressure which produces rollingof the walls, and in consequence a permanent increase in the diameter ofthe tube, while at the same time the tube-mandrel assembly is driven inrotation so as to detach the tubefrom its mandrel, in a delivery channelor any appropriate receiving device.

This operation of mechanical removal of themandrel has a number ofdrawbacks, amongst which may be mentioned:

(1) The considerable time of operation, to which must be added thatrequired for the extraction of the mandrel;

(2) The high capital cost of mandrel-extraction machines, and the highcost of grinding their rollers and of maintenance of their feeding anddelivery channels;

(3) The limitation of use to round tubes only;

(4) The risk of causing scratches or seizures marks on the outersurface, resulting from defects on the rollers and on the positioningwedge, or from whipping of the mandrel during its rotation in the feedand delivery channels;

(5) The increase in the dimensional tolerances obtained during thedrawing operation, which .defect has little influence on the wallthickness but has a sufiicient eflect on the external diameter tonecessitate in all cases a subsequent gauging pass on the hollow tube;

(6) The destruction of the base coatings which have been deposited onthe bare surface of the rnetal before drawing in order to improvetheadherence and the action of the lubricant employed, the disappearance ofthis coating being liable to result in bad lubrication during anysubsequent gauging or drawing pass which is carried out directly afterthe operation of extraction of the mandrel.

The present invention is applied to machines for drawing tubes on longmandrels, in which the tube is provided in known manner with a pointedend at one of its extremities and is tightly engaged on the mandrel atthe end of the drawing operation.

In accordance with the present invention, there is provided in machinesof this type, a mandrel-extraction device comprising in combinationmeans for closing the tubular pointed end in a fluid-tight manner, thusforming a chamber, the internal space of which is at least in partinside the pointed end and communicates with the space comprised betweenthe internal cylindrical wall of the tube and the outer wall of themandrel, and means for introducing a liquid under pressure into theinterior of the said chamber.

Two types of mandrel-extraction devices are envisaged in accordance withthe present invention.

In afirst type, the closure means surround the pointed end externally,at a zone having a generally cylindrical shape.

In a second type of mandrel-extraction device, the closure means areessentially disposed inside the pointed end, at a zone in which thesection is becoming smaller in the direction of the free extremity ofthe pointed end. A closure member placed inside ,the pointed end closesits outer orifice. This closure member is of the autoclave type, sincethe pressure of the fluid introduced inside the chamber closed 'by theclosure member, the inner wall of the pointed end and the outer face ofthe mandrel force the closure member against the inner Wall of thepointed end and thereby increase the sealing effect.

In both types, the fluid may be led inside the chamber by means of aconduit which passes either through the mandrel or through the closuremeans.

The extraction of the mandrel is effected by means of a diametralelastic swelling of the drawn tube subjected to the action oflthe fluidunder pressure, which swelling becomes progressively propagated from theinitial chamber, the fluid under pressure being introduced between themandrel and the tube in such manner that the tube no longer grips themandrel and becomes separated from it in a spontaneous manner so thateither the mandrel may be ejected from the interior of the tube or the.tu'bemay be ejected with respect to the mandrel. The relative move mentis similar to that of a piston with respect to its cylinder.

Experience has shown that the minimum'pressure of the fluid whichproducesthe initial elastic radial deformaamass 1'.

n; 6 tion of the tube can be given to a first approximation by thefollowing formula:

in which:

P=the minimum pressure necessary for the elastic expansion of the tube,expressed in kgs./ sq. cm.;

E=the elastic limit of the material drawn, determined under pure tensionand expressed in kgs./sq. mm.; K=the ratio of the external diameter tothe internal diameter.

By way of example, and without any implied limitation, the applicationof Formula 1 to tubes having an elastic limit of 80 kgs./sq. mm. afterdrawing gives the following values of pressure:

Dimensions of the Drawn Tube in mm.

Internal External Wall K P, kgs./

diam. diam. sq. cm.

102 106 2 l. 039 290 102 104 l 1. 020 150 102 102. 8 O. 4 l. 008 60 5052 1 l. 040 300 50 50. 8 0.4 I. 015 120 50 50. 4 0.2 1. 008 60 3O 321 1. 065 470 30 30. 8 0. 4 1. 026 205 30 30. 4 0. 2 1. 013 100 30 30. 30. 15 1.010 75 12 12. B 0. 4 1. 067 480 12 12. 4 0. 2 1.033 250 12 12. 20. 1 1. 016 125 These examples show that the pressures to be employedbecome smaller, with a constant thickness, as the diameter increasesand, with a constant diameter, as the thickness becomes smaller.

These pressures do not reach excessive values and are within the scopeof standard types of pumps or pressure multipliers which can be obtainedcommercially. The use of a fluid and chemically neutral oil ispreferably recommended so as to facilitate the lubrication of thefluid-tight members and to prevent their corrosion, and also in order tofacilitate the relative movement of the tube and the mandrel at themoment of extraction of the latter.

The description which follows below with reference to the accompanyingdrawings (which are given by way of example only and not in any sense byway of limitation) will make it quite clear how the invention may becarried into effect, the special features which are brought out, eitherin the drawings or in the text, being understood to form a part of thesaid invention.

FIG. 1 shows in a very diagrammatic form, a first type ofmandrel-extraction device in accordance with the invention.

FIG. 2 shows a further form of embodiment of mandrel-extraction device.

FIG. 3 corresponds to a second type of mandrelextraction device inaccordance with the invention and shows very diagrammatically thepointed end of a tube in position on its mandrel, the orifice of thepointed end being internally closed at the moment of introduction of thetube into the die, the tube being actuated during the drawing operationby the mandrel acting under thrust.

FIG. 4 shows diagrammatically the operation of drawing in action withthe device shown in FIG. 3.

FIG. 5 shows the phase of hydraulic mandrel-extraction proper when thedrawing operation has been completed and the mandrel is stationary atthe end of its travel.

FIG. 6 is a view similar to that of FIG. 3, showing a further form ofembodiment of the mandrel-extraction device.

of FIG. 6, the die being assumed to be removed.

FIG. 8 is a view corresponding to that of FIG. 6 of a furtheralternative form of embodiment, in which the tube is actuated during thecourse of drawing by the closure member of the pointed end, acting bytension.

FIG. 9 is a cross-section along the line IXIX of FIG. 8 with the dieremoved.

FIG. 10 is a view similar to that of FIG. 8 but to a smaller scale, andshowing the phase of hydraulic mandrelextraction proper, after thecompletion of the passage of the tube through the die.

In the form of application of the invention shown in FIG. 1, the tube 1is closely fitted and strongly pressed on the long mandrel 2 at the endof one drawing pass. The mandrel is extended into the corresponding partof the end of the tube by a cylindrical portion 3 of smaller diameter,coupled by a chamfer 4 tothe drawn portion 2.

On this portion 3, the tube is formed in a pointed end 5 having athickness greater than that of the tube on the mandrel 2 and an externaldiameter less than that of the said tube. The pointed end 5, by virtueof this thickness, does not adhere to the portion 3 by a compressionwhich would give a permanent deformation, and may be subjected to alocal gripping action without remaining clamped on to the said portion.The portion 3 of the mandrel corresponding to the pointed end 5 ispierced with a longitudinal channel 6 which terminates by at least oneorifice 7 in the region of coupling 4 of the mandrel, for example.

The tube 1 to be extracted from its mandrel is engaged by its pointedend 5 in a hollow head 8 provided with a self-tightening joint showndiagrammatically in the form of a stamped leather 9 engaged around andgripping the pointed end 5. Oil under pressure 10 is supplied to thehead 8 through an orifice 11 and this oil is introduced through thechannel 6 and the orifices 7 between the mandrel 2 and the tube 1 whichit causes to expand elastically, with the result that, since the tube isno longer closely engaged on the mandrel, the latter is thensimultaneously driven out by the action of the pressure on itstransverse section, and frees the tube without further operation. Whenthe pressure is removed, the head 8 can be separated without difficultyfrom the pointed end 5.

In FIG. 2, instead of the mandrel being ejected from the tube by thepressure, the mandrel is held fixed during the operation of extractionand it is the tube which is removed by the pressure of oil.

This solution may be considered as more practical in the case ofmandrels of a certain diameter, the Weight of which is fairly great.

In this alternative form, the mandrel may be either a thick tube with auniform bore, this being easily produced with special steels, or it mayat least be provided over the whole of its length with a passage 12 forthe oil. passage need not necessarily have a machined surface over thewhole of its length, and mandrels of this kind, even of small diameters,can be obtained by compression of tubes or by hollow-drawing of thicktubes of larger diameter, for example.

These mandrels 13 may be simply charnfered at 14, which part comes,during drawing, into contact with the inner end of the pointed end 5,which is kept fairly thick so as to withstand, when empty, the grip ofthe dogs on the drawing machine. During drawing, the pointed end 5 isopen at its extremity 15 and, before the hydraulic extraction of themandrel, it is closed by means of a removable cap 16 of any desiredtype.

The mandrel I3 is connected, for example by a threaded extremity 17 ofthe passage 12, with the source of hydraulic pressure. This pressurepasses into the interior portion of the pointed end 5, and acts asbefore to expand the tube and to move it forward along the fixed mandrelso that it may be freed.

The pointed end may also be closed by bringing its edges together, byflattening, welding, etc.

In the devices shown in' FIGS. 1 and 2, the drawing of the tube throughthe die is effected by tractive force ap-- This plied in known manner tothe pointed end and/ or to the smaller portion of the mandrel inside thepointed end, the hydraulic extraction from the mandrel being effectedduring the course of a separate operation following the drawingoperation proper.

The separation of the operations of drawing and extraction from themandrel with these devices is effected because of the impossibility ofcombining in a single head the gripping members for drawing and thefluid-tight sealing members for the mandrel extraction.

On the other hand, the devices shown in FIGS. 3 to enable these twooperations to be combined, since in this case, the sealing members whichare inside the tubes take part in the drawing action applied to the saidtubes during the course of the drawing operation.

The forms of embodiment of such devices differ essentially by the methodof working of the mandrels which, apart from their function as internalgauges, may act by thrust to draw the tube (see FIGS. 3 to 7) or may, onthe other hand, be actuated by the tube (see FIGS. 8 to 10).

In FIG. 3, the tube before drawing is shown at 1. In accordance with theinvention, the tube is reduced to form an offset 20, by means of acompressing machine, for example. This offset 20 is followed, in thisexample, by a cylindro-spherical portion 21 which terminates axially inan orifice 22 opening into the exterior and reinforced by a droppededge.

The depth of the cylindro-spherical housing 21 is slightly less than itsdiameter, so that, at the moment when the mandrel 2 comes into contactwith the offset 20, a sphere 23 of rubber or other similar material ispushed by the end 24 of the mandrel and is forced into contact againstthe base which carries the orifice 22.

This sphere 23 has substantially the same diameter as the interior ofthe cavity 21. At this moment, the periphery of the offset 20 is engagedin the die 25, and as a result of its forward movement, the mandrel 2,of which the periphery of the end 24 has come into contact with theinterior of the offset 20 drives the tube 1 through the die and effectsthe drawing operation. The offset 20 is able, due to its shape, towithstand the thrust of the mandrel 2 without being deformed, and totransmit this thrust to the tube 1 during is passage through the die, inaccordance with known practice.

The mandrel 2 is fixed on the moving portion 26, a jack for example, ofthe drawing press, on the bed of which is fixed the die 25, this pressbeing of known type and not being shown in the drawing. This mandrel hasa channel 12 passing throughout its length, the channel being coupledexternally at 27 to a source of liquid under pressure which iscontrolled so as to admit the liquid after the tube has been drawn byits complete passage through the die (see FIG. 4).

In addition to the central conduit, it is preferable to provide themandrel with pierced holes such as 28 which open into the centralconduit and end close to the offset 20, without being closed thereby, soas to ensure communication of the passage 12 with the cavity.

The pressure of this liquid forces the sphere still more strongly in thecavity 21 and reinforces its closing action at 22. This pressure canthus act effectively for the hydraulic extraction of the tube 1, whichis ejected from the mandrel 2 which is freed from it.

The tube is then emptied of liquid, and the sphere 23 is ejected from itby the simple action of compressed air applied through the orifice 22.

During drawing, and before and after the drawing operation, the mandrelremains always fixed on the drawing press, together with all the devicesfor supporting it and preventing it from buckling, as the case mayrequire. It is thus protected from any handling operation which mightresult in risk of damage, and its retains an outer surface with a veryhigh degree of polish, resulting in a perfect finish and facilitatingthe extraction operation.

A same housing profile for the closure member may be employed for acertain range of diameters of tubes,

the maximum radius of the offset 20 being the only varying factor as aresult of each drawing, over a whole series of passes. A certain economyis thus obtained with respect to the use of ordinary or special pointedends which are normally employed. The only manipulation of carrying,moving and introduction of pieces is that of the light tubes and this ismuch simpler than the handling of heavier mandrels, any damage to whichwould effectively prevent their further use,

While the spherical form of the closure member would appear to be themost satisfactory, any form of housing could of course be employed forcarrying out the invention which is adapted to, receive a closure devicewhich can be put automatically in position internally, and with whichthe hydraulic pressure produces an autoclave type of closure: such asconical, cylindro-conical or prismatic plugs in the case of polygonaltubes, or plugs of any section appropriate to that of the tube, whichcan be drawn in shapes other than cylindrical shapes of revolution, onmandrels and with dies of corresponding shape.

These plugs will be of elastic and deformable material, of a compositionwhich is firm enough *to permit of their guiding and easydelivery by themandrel. In certain cases, they may be of mixed form, having a metalsupporting portion for example and an elastic supporting surface for theautoclave closure. In particular, spherical closure valves may beprovided with an inner spherical core of steel, covered with a layer ofelastic material.

Tests have shown that the use of a plug made entirely of an indeformablematerial may have certain advantages, especially, in the case of verythin tubes. In order to ensure the maintenance of the plug in position,the most simple expedient. is to cause it to be subjected to the thrustof the mandrel. The presence of an offset on the tube is no longernecessary, and this absence of offset avoids the occurrence of thephenomenon known by the term cuff, and which consists in an excessivecoldrolling of the thicker zone of the offset. Mandrel-extractiondevices with rigid plugs are shown in FIGS. 6 and 7.

The pointed end of the tube 1 consists of a body of revolution 30, inthis case conical over its whole length between its coupling, withoutany sharp variation, at 31 with the tube 1 and its parallel couplingportion, at 32 Where it is tangential .with the spherical zone 33provided with the orifice 22 at the end, which opens into the reducedtubular portion 22a which extends, with an abrupt change indirection,the orifice 22, the latter .being thereby strongly reinforced.

Inthe spherical FZOllG 32 is housed a ball 23 of very hard and perfectlypolished "steel, in practice a bearing ball, having the same diameter das the spherical zone 33 and being subjected to the thrust of themandrel '2. The ball 23 is automatically centered in the spherical zone33 and in a conical seating 34 formed in the outer face 24 of themandrel '2.

In the face24, a milled transverse slot 35 opens into the 'chamfer 36 ofthe extremity of the mandrel, and allows free access of the liquid underpressure which is brought through the mandrel by the passage 12, intothe space 37.

The pressure of this liquid enables the hydraulic extraction of themandrel to be effected in the knowntmanner. The internal diameter of thetube to be drawn being D, the diameter d of the ball 23 will remainalways in practice between D, reduced by the quantity necessary for apre-determined series of successive drawing operations, and a minimumwhich will be greater than of the initial diameter D, which can beexpressed:

The operation is quite obvious: the pointed end being introduced intothe die 25 (see FIG. 6), the ball 23, pushed into the tube and into thepointed end by the mandrel 2, is powerfully applied against thespherical zone 33 and ensures a perfect closure of the orifice 22 whileat the same time the thrust of the mandrel applied to the pointed end inthis zone 33, is transmitted to the tube 12 by the coupling portionwhich works under tension. The tube is thus forced through the die 25 bythe mandrel 2 and is drawn.

The progressive compression of the portion 3132 of the pointed end hasthe result that, after the first pass consecutive to the formation ofsaid end, there is no sharp variation in thickness due to an increase inthickness, as is the case with the abrupt offsets which serve to supportthe mandrel in the known methods.

The tangential angle of the tube at the moment of initiation of drawingin the die remains practically constant and small during the successivepasses with the same pointed end and the same ball, the die and themandrel being possibly changed a certain number of times. In addition,the progressive nature of this opening phase is accompanied by acharnfer 36 with a fairly small angle. In this way, all cuff effect isavoided, this effect being the cause of ruptures during the course ofthe hydraulic mandrel extraction which follows each drawing pass of thetube.

When the liquid under pressure is brought at 12 into the space 3737 forthe purpose of mandrel extraction, the ball 23 which closed the orifice22 by the pressure which it received from the mandrel and which ismaintained after passing through the die, by the adherence of the tubeon the mandrel, continues to remain in position during the extraction ofthe mandrel, in the spherical zone 33 by the autoclave effect due to thepressure of the liquid which carries out this mandrel-extractionoperation in the known manner.

When the extraction has been completed, after evacuation of the liquid,the ball 23 is pushed back out of the tube which is to be annealed, andis removed in order that it may be re-introduced for the next pass. Thisball detaches itself readily and has no tendency to remain stuck bypenetration into the open portion 22a. As a last resort, in the case ofa coupling with a very small angle which may cause a certain jamming ofthe ball, the latter may be easily dislodged in this exceptional case byany known means.

The use of a polished ball enables the latter to move inside the tubewhen it is introduced and be removed without causing the slightestscratch in the tube surface.

This device enables very thin tubes to be drawn with a very smallpercentage of waste during manufacture, in spite of the difiiculties ofthis type of manufacture. Alternative forms of the pointed end, in themanner of constructing the spherical zone and in the machining of theextremity of the mandrel may, of course, be employed in the presentdevice without departing from the scope of the invention.

The pointed end may be made in the form of an elongated section of acone, open at its small base and coupled to the tube without any offset.

The spherical zone may be formed by the actual forcible introduction ofthe indeformable ball itself under the thrust of the mandrel, whichmakes an impression in the said cone until the resistance becomes equalto the force required for passing the tube through the die on themandrel which drives it.

The spherical zone formed in this way will not progress forward to anygreat extent during the following passes, and in practice, slightvariations due to this small progression will not have any effect.

In order to avoid any abnormal local stress applied to the ball by themandrel, there may be an advantage in replacing the conical opening 34by a hollow spherical opening having the same radius as that of theball, the communicating passages 35 between the bore 12 and the space 37remaining of course unclosed when the ball is pressed into the saidspherical opening.

Experience has shown that the use of the device shown in FIGS. 3 to 7has limits in the case of tubes of large lengths or of small diameters,by reason of the difliculties of boring the mandrels and the complexarrangements which must be employed to avoid buckling of the saidmandrels during the drawing operation.

It should be observed that in the device shown in FIGS. 6 and 7, thetractive effort which produces the drawing of the tube is applied to itby the closure member. The mandrel constitutes on the one hand amechanical coupling member acting by thrust between the closure memherand the driving jack, and on the other hand the hydraulic couplingmember between the fluid-tight chamber inside the pointed end and thesource of fluid under pressure. The limitations of use referred to aboveno longer exist if the closure member is driven by a mechanical couplingmember acting under tractive force, the mandrel being then simply drivenby the tube by the effect of gripping which results from the drawingaction. This mechanical coupling member may further constitute ahydraulic coupling member.

A device of this kind is shown in FIGS. 8 to 10. As in the case of FIGS.6 and 7, the tube 1 which is to be drawn is terminated by a hollow openpointed end, constituted in known manner by a generally conical coupling30 between the tube 1 and a spherical Zone 33 opening into a circularorifice 22, extended by a tubular reinforcing portion 22a.

Into this pointed end is passed a traction member 40 terminating in ahead 41 which is partly spherical with the same radius as the sphericalzone 33. This head is extended through the orifice 22 and passes beyondthe tubular portion 22a in the form of the body 40, in this casecylindrical, with the angle of its extremity rounded at 42. The part ofthe head 41 opposite to the body 40 is in this case limited by a flatface 43, perpendicular to the axis of the body 40 in a transverse planewhich, when the head 41 is in position, that is to say in contact withthe spherical zone 33 of the pointed end, cuts through the conicalcoupling portion 30 of the said pointed end. The fiat transverseextremity 24 of the mandrel 2 is n contact with this flat face 43. Thistransverse extremity 1s chamfered at 36 over a length and at an anglewhich then permits its free penetration into the commencement of thecoupling portion 30 of the tube 1.

In order to effect a strictly coaxial alignment of the mandrel 2 and thetractive member 40, the face 24 of the mandrel is provided with acylindrical cavity 44 in which s fnctionally engaged a cylindricalextension 45 which is split in two halves by a cut 46 milled along adiametral plane, this cut forming in the face 43 of the head 41 adiametral groove 47 opening into the annular space 24 remaining freebetween this head 41, the extremity of the mandrel 2 and couplingportion 30 of the hollow pointed en The tractive member 40, the head 41and the cylindrical extension 45 have passing through them from one endto the other a bored axial passage 48 which leads the fluid underpressure into the space 24 for the hydraulic extraction of the mandrel,this fluid being, in general, oil.

The mandrel 2 will be provided with the tractive member 40 fitted intoits extremity by its portion 45 forced fully into the housing 44 whichwill be slightly chamfered at ts free extremity together with the part45 in order to facilitate a tight driving fit, without howevernecessitating any other operation but driving-in by hand. The mandrelextended in this manner will be forced into the tube 1 (or converselywill be covered by the tube which is passed over it) before beingmounted on the drawing machine, the pointed end in contact in the die 25through which it passes, and the rod 40 extending beyond and in front ofthe said pointed end. The extremity of this rod is gripped and fixed inthe moving member which will draw the whole assembly in tension throughthe said die.

In the example shown, the tractive effort is transmitted to the rod 40by a hollow sleeve 49 actuated for example by the chain of thedraw-bench (not shown) in the same way as a conventional type of drawingdog, in the direction of the arrow 50. For that purpose, the hollowsleeve 49 which receives the rod 40 ina bore 51 having a diametercorresponding to that of the rod 40, is provided with mechanicalself-clamping fixing means of known type indicated in this case by jawsin the form of toothed wedges 52 displaceable in a conical housing 53located close to the rear extremity (in the direction of movement 50) ofthe sleeve 49.

In front of this mechanical actuating clamp, external fluid-tighmessaround the rod 40 in the bore 51 is effected by means of a usual kind oftoric joint 54, housed in a circular groove 55 of the sleeve 49.

At the front, the sleeve is closed and provided with an axial hole 56which can be coupled through a threaded portion 57 with a flexibleconduit (not shown) provided for the supply, in a manner controlled byknown means which are therefore not described, of the oil under pressurewhich passes into the conduit system 48. The pres- Sure of this oilreinforces the tightness of the joint 54 in known manner by an autoclaveeffem.

The method of operation will be clear: the rod 40 being actuated by themovement of the sleeve 49 in the direction of the arrow 50, forces thetube 1 through the die 25 by the pressure of the head 41 in thespherical zone 33 of the pointed end. The driven tube passes into thedie 25 and is drawn between the die and the mandrel 2 which moves withthe head 41.

The gripping action of the tube during its passage through the die fixesthe tube on the mandrel, which of course accompanies the tube and thehead of the extension piece.

The travel of the liquid, generally oil, which is introduced at aregulated pressure so as to effect a freeing action by elastic expansion(thus very limited) of the tube between the mandrel and the tube, is notinstantaneous, and its progress along the whole length of the tube wouldresult in a waste of time, if the operator waited until the tube hadpassed out of the die before admitting the oil at the extractionpressure into the said tube, between the chamfered end of the mandrel,the head 41 and the tube.

As soon as the tube has been drawn over a fairly short length betweenthe mandrel and the die, the oil under pressure is permitted to passthrough the extension mem- The length of extension beyond the die willobviously vary, depending on the tube to be drawn, and it is chosen as aresult of experience to be as small as possible; in general, this lengthwill be of the order of a decimeter, independently of the length of thetube to be drawn.

The closure, apart from any tractive effort, is maintained by theautoclave effect of the head forced into the pointed end by theextraction pressure, and as soon as the tube has passed out of the die25, the forward movement of 49 in the direction 50 can be stopped. Whenthe flow of oil between the mandrel and the elastically expanded tube,reaches the extreme portion of the tube, the mandrel 2 will be rapidlyejected towards the rear, in the direction of the arrow 60, through thedie 25.

The rod 40 of the tractive member will be separated from the sleeve 49by means of release of the jaws 52, these means being known and notbeing shown, and, the pressure of the oil having fallen and its entry at56 closed, the joint 54 which ensured the fluid-tight seal no longeroffers any resistance to the return movement of the rod 40 which will bepushed into the tube through the pointed end, to be removed fromthe rearwithout difficulty, and without damaging the tube, in which theextension member rests only on smooth and rounded parts.

In the device described, the closure is effected directly by thespherical portion of polished hard steel, engaged in the correspondinghousing in the pointed end.

In fact, if this is useful, and this is especially the case in thedrawing of tubes having other than circular sections, for which theenlarged portion which constitutes the (head is more difiicult toaccommodate in a concave corresponding coupling-in the pointed end, itmay be necessary to utilise an elastic portion lining the head of thetractive member so as to ensure a fluid-tight support of this member.The presence of the tension rod 40 which actuates the head through thetubular portion 22 enables practically all extrusion of the elasticlining portion of the head through the opening of the pointed end to beprevented, by leaving a fairly small clearance between this rod and itspassage into the said tubular portion.

This permits of less accurate machining of the head of the tractivemember which constitutes a very advantageous feature, in particular inthe case of tubes of small dimensions and for tubes of polygonalsections or other than circular form, and thus enables the method of thepresent invention to be applied to these sections.

Without departing from the scope of the invention, the temporary fixingof the long mandrel to the head of the extension member may be effectedby any means other than that shown, and may not be effected before theplacing in position of the mandrel and the extension memher.

In this case, a simple magnetic grip may be employed, or even a slightthrust applied to the mandrel so as to maintain it in contact with thehead at the beginning of its passage through the die.

The tractive member may be brought into position by the thrust of themandrel and will center itself at the beginning of the passage throughthe die. The rod of the tractive member, which is generally cylindrical,may very well be provided with transverse grooves or other means, whichdo not exceed the corresponding diameter of the outlet opening of thepointed end, for effecting its actuation by tractive effort.

The injection of oil under pressure could in the same way have its inletindependent of the fixing of the rod of the tractive member on thedrawing apparatus, the liquid under pressure being admitted through alateral special coupling, for example to pass into the rod, or axiallyin front of the rod-actuating member through which the rod thencompletely passes and is provided with an instantaneous coupling ofknown type.

By reason of the hydraulic mandrel-extraction device, the tubes producedare tested at the same time for pressure tightness, and those which donot show any leakage (which would furthermore prevent their automaticremoval from the mandrel), when the tube is detached over its wholelength by the pressure of the liquid producing the extraction, are tubeswhich are tested and perfectly sound. This represents a very importantstep in the progress of this technique.

What I claim is:

1. In a machine for drawing tubes comprising a die and an elongatedmandrel adapted to cooperate with said die for drawing a tube disposedover said mandrel and having an open pointed end, said pointed endhaving a spherical zone; a closure member located inside said tube andhaving a spherical surface corresponding with said zone, and radialchannel means for introducing a liquid under pressure into said tubebetween said mandrel and said member, said means comprising a bore insaid closure member and in communication with the interior of said tube,and means for connecting said bore to a source of fluid under pressureto force fluid into said tube to loosen said mandrel therefrom.

2. In a machine for drawing tubes comprising a die and an elongatedmandrel adapted to cooperate with said die for drawing a tube disposedover said mandrel and having an open pointed end, the combination of aclosure member having a part spherical head located within said pointedend and a body protruding through said pointed end, said member piercedwith a bore extending through said head and body and in communicationwith the interior of said tube, a spherical zone in said pointed end,registering with at least a part of said spherical head; means fortemporarily coupling said mandrel and said closure member; means forgripping said body and exerting a traction on it and means forconnecting the bore in said member to a source of fluid under pressureto force fluid into said tube to expand it and loosen said mandreltherefrom.

References Cited in the file of this patent Kum'holm Oct. 18, 1955 HohlNov. 19, 1957

1. IN A MACHINE FOR DRAWING TUBES COMPRISING A DIE AND AN ELONGATEDMANDREL ADAPTED TO COOPERATE WITH SAID DIE FOR DRAWING A TUBE DISPOSEDOVER SAID MANDREL AND HAVING AN OPEN POINTED END, SAID POINTED ENDHAVING A SPHERICAL ZONE; A CLOSURE MEMBER LOCATED INSIDE SAID TUBE ANDHAVING A SPHERICAL SURFACE CORRESPONDING WITH SAID ZONE, AND RADIALCHANNEL MEANS FOR INTRODUCING A LIQUID UNDER PRESSURE INTO SAID TUBEBETWEEN SAID MANDREL AND SAID MEMBER, SAID MEANS COMPRISING A BORE INSAID CLOSURE MEMBER AND IN COMMUNICATION WITH THE INTERIOR OF SAID TUBE,AND MEANS FOR CONNECTING SAID BORE TO A SOURCE OF FLUID UNDER PRESSURETO FORCE FLUID INTO SAID TUBE TO LOOSEN SAID MANDREL THEREFROM.